Ok, I admit it. I am not an expert on English. Sometimes, I misue commas. Sometimes, I even spell words wrong. However, it seems like your average person no longer cares about writing correctly. I get e-mails at work with many misspellings, improper punctuation, and–yes–even incorrect word use (your for you’re, there for their, etc…). These people are making basic mistakes that they should have learned about in the 5th and 6th grade. I came across this site today that talks about gramatical rules. If you notice, it is a .uk domain, so the content is not geared for American English; however, I read it and think that most of the rules are the same. They do use some different terminology (full stop for period) and they have several words spelled the “British” way. Enjoy!
[Update 2012-12-26 15:04:18] The “this” site mentioned is now a dead link. It went to http://www.bim.napier.ac.uk/~hazel/gen_ho/rules_conv.htm